Reading circuit for a multi-axis MEMS gyroscope having detection directions inclined with respect to the reference axes

ABSTRACT

A multi-axis gyroscope includes a microelectromechanical structure configured to rotate with respective angular velocities about respective reference axes, and including detection elements, which are sensitive in respective detection directions and generate respective detection quantities as a function of projections of the angular velocities in the detection directions. The gyroscope including a reading circuit that generates electrical output signals, each correlated to a respective one of the angular velocities, as a function of the detection quantities. The reading circuit includes a combination stage that combines electrically with respect to one another electrical quantities correlated to detection quantities generated by detection elements sensitive to detection directions different from one another, so as to take into account a non-zero angle of inclination of the detection directions with respect to the reference axes.

BACKGROUND

1. Technical Field

The present disclosure relates to a reading circuit for a multi-axis MEMS gyroscope having detection directions inclined with respect to the reference axes, and to a corresponding multi-axis MEMS gyroscope.

2. Description of the Related Art

As is known, micromachining techniques enable manufacturing of microelectromechanical structures or systems (MEMS) within layers of semiconductor material, which have been deposited (for example, a polycrystalline-silicon layer) or grown (for example, an epitaxial layer) on sacrificial layers, which are removed via chemical etching.

Inertial sensors, such as accelerometers and gyroscopes, made using this technology are experiencing an increasing success, for example in the automotive field, in inertial navigation, or in the sector of portable devices.

In particular, integrated gyroscopes made of semiconductor material using MEMS technology are known. These gyroscopes operate on the basis of the theorem of relative accelerations, exploiting Coriolis acceleration. When an angular motion is applied to a mobile mass that is driven with a linear motion, the mobile mass “feels” an apparent force, called Coriolis force, which determines displacement thereof in a direction perpendicular to the direction of the linear motion and to the axis about which the angular motion is applied. The mobile mass is supported via springs that enable its displacement in the direction of the apparent force. On the basis of Hooke's law, the displacement is proportional to the apparent force so that, from the displacement of the mobile mass, it is possible to detect the Coriolis force and the value of the angular velocity that has generated it. The displacement of the mobile mass may for example be detected in a capacitive way, by determining, in conditions of resonance, the variations of capacitance (or, likewise, of the amount of charge) caused by the movement of mobile electrodes, fixed with respect to the mobile mass (or constituted by the mobile mass itself) and coupled to fixed electrodes.

MEMS gyroscopes have generally symmetrical sensing structures, comprising a pair of sensing masses for each reference axis about which a corresponding angular velocity is detected, the sensing masses being aligned to one another in a detection direction (generally coinciding with a corresponding reference axis). The reading circuit hence generally adopts a differential scheme based upon the differential capacitive variations associated to the sensing masses of each pair. In fact, whereas the Coriolis force tends to unbalance in opposite directions and substantially by the same amount the sensing masses of each pair (generating so-called “phase opposition” movements), external noise accelerations determine displacements thereof in the same direction and again by the same amount (generating so-called “in-phase” movements). By computing the difference of the electrical signals associated to the two sensing masses of each pair, it is hence ideally possible to isolate and measure just the contribution due to the Coriolis force and completely reject the contributions of noise.

For example, a biaxial MEMS capacitive gyroscope detects a first angular velocity directed along a pitch reference axis, designated in what follows by x, and a second angular velocity directed along a roll reference axis, designated hereinafter by y. By applying the Coriolis theorem, the following expressions are obtained: M _(c)=−2·J·Ω _(x)

ω_(z) ;M _(c)=−2·J·Ω _(y)

ω_(z) where M_(c) is the moment of the Coriolis force acting upon the sensing masses (which, as will be described in greater detail hereinafter, perform a detection movement of rotation out of the plane of the sensor), J is the moment of inertia of the same sensing masses, Ω_(x) and Ω_(y), are the unknown angular velocities of pitch and roll acting about the respective reference axes, and ω_(z) is the driving angular velocity of the driving motion, directed along a vertical axis z (orthogonal to the plane of the sensor) and variable for controlling an electromechanical driving loop of which the MEMS structure of the sensor forms an integral part (the driving angular velocity also acting as a constant scale factor in the aforesaid expressions). In particular, this driving loop is made by an integrated circuit dedicated to generating and maintaining a movement of oscillation of a driving mass, to which the sensing masses are mechanically coupled, with driving angular velocity ω_(z) and at the resonance frequency.

The reading circuit of the gyroscope, as described for example in US Patent Application Publication Nos. US2008190200 and US2007289382, assigned to STMicroelectronics Srl, is configured so as to read, through the differential capacitive variation associated to the pitch or roll sensing masses, a signal proportional to the vector product Ω_(x)

ω_(z), in the case of pitch, or Ω_(y)

ω_(z), in the case of roll, the signal being of a DSB-SC (Dual Side Band-Suppressed Carrier) type, i.e., amplitude-modulated with a carrier given by the driving angular velocity ω_(z), due to driving of the structure at the resonance frequency. Next, by means of a coherent demodulation, the signal is first brought into baseband and then appropriately filtered, obtaining at output an electrical signal (in particular, a voltage signal) proportional to the unknown quantity alone, namely the pitch angular velocity Ω_(x) or the roll angular velocity Ω_(y).

In greater detail, and as illustrated in FIG. 1, the reading circuit, here designated by 1, has two distinct transduction chains, a first transduction chain, designated by 1 a, for detection of the pitch angular velocity Ω_(x) and a second transduction chain, designated by 1 b, for detection of the roll angular velocity Ω_(y). Also indicated in FIG. 1 are the contact of the mobile (or rotor) electrodes Rot, in common to all the sensing masses, the contacts of the fixed (or stator) electrodes P₁, P₂ associated to the pair of pitch-sensing masses, and of the fixed electrodes R₁, R₂ associated to the pair of roll-sensing masses (as well as the corresponding pairs of capacitors, having a capacitance variable in a differential manner). In particular, FIG. 1 shows the case where a single fixed electrode is associated to each sensing mass. Furthermore, an excitation signal, for example a voltage step ΔV_(S), is applied to the mobile electrodes Rot during reading operations.

Each transduction chain 1 a, 1 b, of a fully differential type and made using the switched-capacitor (SC) technology, comprises:

-   -   a charge amplifier 2, i.e., a charge/voltage converter, designed         to minimize noise contributions and designed to convert the         differential capacitive variation received at input (due to the         displacement of the mobile electrodes with respect to the fixed         electrodes) into a voltage variation signal of a fully         differential type, this signal being a signal of a DSB-SC type         on account of driving at the resonance frequency of the driving         mass; the charge amplifier 2 has for this purpose a positive         input and a negative input connected to a respective fixed         electrode P₁, P₂ of the sensing masses;     -   a demodulator (or mixer) 4, cascaded to the charge amplifier 2         and forming therewith a measurement chain for signals of a         DSB-SC type of the transduction chain, which is designed to         carry out coherent demodulation of the amplitude-modulated         signals of a DSB-SC type; in particular, by means of a clock         signal CK in phase with the carrier of the signal (the driving         angular velocity ω_(z)), previously processed so as to minimize         its phase delay, a coherent demodulation is obtained such as to         bring the output signal, once again of a fully differential         type, into baseband and reject the spurious components         superimposed on the same signal (which have the same carrier         frequency but are out of phase with respect to the information         component by an angle of 90°);     -   a sample&hold stage 6, cascaded to the demodulator 4 and         designed using the switched-capacitor (SC) technique, which has         the purpose of transforming the fully-differential demodulated         signal into a single-ended signal; and     -   a filter stage 8, which is cascaded to the sample & hold stage 6         to form a measurement chain for baseband signals of the         transduction chain and is designed to implement a transfer         function of a second-order lowpass filter so as to reject all         the undesirable components that fall outside the band of         interest of the signal (typically up to 140 Hz), amongst which         the known components, which, as a result of coherent         demodulation, are at the resonance frequency (so-called residual         offset) and at a frequency equal to twice the resonance         frequency, and supply at output a useful analog signal OUT (of         pitch or of roll) on a purposely provided output electrode 9 a,         9 b; the output signal contains the desired information of the         pitch or roll angular velocity detected by the MEMS capacitive         gyroscope.

BRIEF SUMMARY

The present Applicant has found that the reading circuit previously described is not, however, usable in the case where the multi-axis gyroscope has detection directions that do not coincide with its reference axes, being for example inclined by a given angle with respect to the reference axes.

One embodiment is a reading circuit that is able to operate in the case where the detection directions of the sensor are inclined with respect to the corresponding reference axes (for example, the axes of pitch and roll).

One embodiment is a multi-axis gyroscope that includes a microelectromechanical structure configured to rotate with respective angular velocities about respective reference axes, and a reading circuit. The microelectromechanical structure includes first and second detection elements sensitive along first and second detection directions, respectively, the first and second directions being different from one another, and are configured to generate respective detection quantities as a function of projections of the angular velocities in the first and second detection directions, the first detection directions being inclined with respect to the reference axes by a non-zero angle of inclination. The reading circuit includes: a combination stage configured to combine electrically together electrical quantities correlated to detection quantities generated by the first and second detection elements, so as to take into account the non-zero angle of inclination of the first and second detection directions with respect to the reference axes; and an output stage configured to provide electrical output signals based on combined electrical quantities received from the combination stage, each signal being correlated to a respective one of said angular velocities.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a better understanding of the present disclosure, preferred embodiments thereof are now described, purely by way of non-limiting example and with reference to the annexed drawings, wherein:

FIG. 1 shows a schematic block diagram of a reading circuit of a multi-axis MEMS capacitive gyroscope, of a known type;

FIG. 2 shows a schematic top plan view of a microelectromechanical structure of a multi-axis MEMS capacitive gyroscope;

FIG. 3 shows a schematic and simplified representation of a portion of the gyroscope of FIG. 2;

FIG. 4 shows a schematic block diagram of a reading circuit of a multi-axis MEMS capacitive gyroscope, according to a first embodiment of the present disclosure;

FIG. 5 shows in greater detail the implementation of a combination stage in the circuit of FIG. 4;

FIG. 6 shows a schematic block diagram of a reading circuit of a multi-axis MEMS capacitive gyroscope, in accordance with a second embodiment of the present disclosure; and

FIG. 7 shows a block diagram of a MEMS capacitive gyroscope and of a corresponding electronic device, according to a further aspect of the present disclosure.

DETAILED DESCRIPTION

Italian patent application TO2008A000876, from which the present application claims priority, discloses an integrated microelectromechanical gyroscope sensitive to angular velocities along three reference axes, pitch, roll and yaw, where the detection directions (i.e., the directions along which the sensing masses are sensitive) are inclined with respect to the reference axes by a given (nonzero) angle, in particular by an angle equal to 45°.

This gyroscope proves particularly advantageous in so far as it enables the MEMS structure and the corresponding electrical connections to be more symmetrical, rationalization of the area occupied, and maximization of the sensitivity of detection of the angular velocities.

FIG. 2 shows, for example, an embodiment of a MEMS structure of a multi-axis gyroscope, designated by 10, made according to the teachings contained in the aforesaid Italian patent application.

The MEMS structure 10 is provided in a die 12, comprising a substrate 12 a of semiconductor material (for example, silicon), and a frame 12 b defining within it an open region 12 c, overlying the substrate 12 a, which is to house the sensing structures of the multi-axis gyroscope. The open region 12 c has a generically square or rectangular configuration in a plane of the sensor xy (substantially parallel to the plane of the substrate 12 a), defined by a first horizontal axis x and by a second horizontal axis y fixed with respect to the die 12; the frame 12 b has sides substantially parallel to the horizontal axes x, y. Die pads 12 d are arranged along at least one side of the frame 12 b, aligned, for example, along the first horizontal axis x. In a way not illustrated, the die pads 12 d enable electrical contact from outside of the sensing structures of the multi-axis gyroscope. The die pads 12 d moreover have an axis of symmetry, in this case coinciding with the second horizontal axis y (which is orthogonal to their direction of alignment). In particular, the first and second horizontal axes x, y correspond to the pitch and of roll reference axes of the MEMS structure 10, around which the angular velocities of pitch Ω_(x) and roll Ω_(y), are detected.

The MEMS structure 10 comprises driving elements, housed within the open region 12 c and including a driving mass 13 and a driving assembly 14.

The driving mass 13 has a substantially planar configuration with main extension in the plane of the sensor xy, and negligible size, with respect to the main extension, in a direction parallel to a vertical axis z, forming with the first horizontal axis x and the second horizontal axis y a set of three orthogonal axes (the vertical axis z moreover coinciding with the yaw reference axis of the MEMS structure 10). The driving mass 13 defines at the center an empty space 16, the center O of which coincides with the centroid and the center of symmetry of the entire structure. The driving mass 13 is moreover anchored to the substrate by means of a first anchorage 17 a, set within the empty space 16, to which it is connected through first elastic anchoring elements 18 a, and by means of further anchorages 17 b, which are arranged outside the same driving mass 13 and to which the latter is connected by means of further elastic anchoring elements 18 b. The elastic anchoring elements 18 a, 18 b enable a movement of rotary oscillation of the driving mass 13 about a driving axis passing through the center O, parallel to the vertical axis z and perpendicular to the plane of the sensor xy, with driving angular velocity ω_(z).

The driving mass 13 moreover has: a first pair of through openings 19 a, 19 c, which are aligned in a diametral direction in a first detection direction x₁, inclined with respect to the first horizontal axis x of the die 2 (coinciding with the pitch reference axis) by an angle of inclination Θ (considered in a counterclockwise direction), the value θ of which is preferably 45°, and are arranged on opposite sides with respect to the empty space 16; and a second pair of through openings 19 b, 19 d, which are aligned in a diametral direction in a second detection direction x₂, substantially orthogonal to the first detection direction x₁, and inclined with respect to the first horizontal axis x by the same angle of inclination Θ (considered in this case in an opposite, clockwise, direction), and are also arranged on opposite sides with respect to the empty space 16. In particular, each through opening 19 a-19 d has in the plane of the sensor xy the shape of a radial annulus sector, having arc-shaped inner and outer sides and radially extending lateral sides. The driving mass 13 moreover has a pair of further through openings 20, 20′, having in plan view a substantially rectangular shape, and aligned along the second horizontal axis y (or, alternatively and in a way not illustrated, along the first horizontal axis x), and having a main extension in a direction transverse to the horizontal axis.

The driving assembly 14 comprises a plurality of sets of driving electrodes 21, extending outside the driving mass 13 in a radial direction and in a way angularly spaced at equal distances apart, constituted by electrodes in comb-fingered configuration. Suitable electrical biasing signals coming from an electronic driving circuit (here not illustrated), determine, by means of mutual and alternating attraction of the electrodes, the oscillatory rotary movement of the driving mass 13 about the vertical driving axis z, at a resonance frequency of oscillation and at the driving angular velocity ω_(z).

The MEMS structure 10 further comprises a first pair of acceleration sensors with axis parallel to the vertical axis z, and in particular a first pair of sensing masses 22 a, 22 c, arranged within a respective through opening 19 a, 19 c of the first pair so as to be completely enclosed and contained by the overall dimensions of the driving mass 3 in the plane of the sensor xy. Each of the sensing masses 22 a, 22 c has a shape corresponding to that of the respective through opening, and consequently has, in plan view, the generic shape of a radial annulus sector. Each of the sensing masses 22 a, 22 c is moreover supported by a pair of elastic supporting elements 24 extending within the respective through opening in a direction transverse to the first detection direction x₁, so as to be suspended on top of the substrate 12 a. The elastic supporting elements 24 form torsional springs, which are rigid in regard to the rotary motion of the driving mass 13 (so that the sensing masses 22 a, 22 c follow the driving mass 13 in its driving motion), and moreover enable rotation of the sensing masses about an axis of rotation parallel to the direction of extension of the elastic supporting elements 24, and hence their movement out of the plane of the sensor xy (a movement that is not, instead, allowed for the driving mass 13).

In a similar way, the MEMS structure 10 comprises a second pair of acceleration sensors with axis parallel to the vertical axis z, and in particular a second pair of sensing masses 22 b, 22 d, housed within the through openings 19 b, 19 d of the second pair.

The sensing masses 22 a-22 d are consequently aligned in respective detection directions x₁, x₂, which are inclined with respect to the pitch and roll reference axes, about which act the angular velocities to be detected, and are moreover inclined with respect to the sides of the die 12 (parallel to the same reference axes). On the basis of the Coriolis theorem, the sensing masses are hence sensitive to angular velocities acting in the respective detection directions x₁, x₂.

A respective fixed electrode 25 is set underneath each of the sensing masses 22 a-22 d, for example constituted by a region of polycrystalline silicon formed on top of the substrate 12 a. The fixed electrodes 25 form, with the respective sensing masses, sensing capacitors, having capacitance that is variable as a function of the displacement of the sensing mass itself due to the Coriolis force (and hence as a function of the angular velocity to be detected); in particular, the same sensing masses constitute the mobile electrodes of the sensing capacitors. The fixed electrodes 25 are connected to the reading circuit of the multi-axis gyroscope (here not illustrated) via the die pads 12 d; in addition (in a way not illustrated), the sensing masses are electrically connected together and connected to a single electrical contact, which is also coupled to the aforesaid reading circuit via the die pads 12 d.

The MEMS structure 10 further comprises a pair of further sensing masses 28, 28′ housed within the further through openings 20, 20′, suspended with respect to the substrate 12 a and connected to the driving mass 3 via respective elastic supporting elements 29. In particular, the elastic supporting elements 29 are rigid with respect to the driving motion of the driving mass 13 (so that the further sensing masses 28, 28′ follow the driving mass 13 in its movement of rotary oscillation) and moreover enable a linear movement of the respective sensing masses, in the case represented along the second horizontal axis y, in response to the centrifugal force. Coupled to each of the further sensing masses 28, 28′ are mobile electrodes, which form sensing capacitors with plane and parallel faces with respective fixed electrodes 25, fixed with respect to the driving mass 13.

In use, the MEMS structure 10 is able to operate as a triaxial gyroscope and to detect the angular velocity of pitch Ω_(x) about the first horizontal axis x, the angular velocity of roll Ω_(y) about the second horizontal axis y, and an angular velocity of yaw Ω_(z), acting about the vertical axis z.

The pitch angular velocity Ω_(x) or, likewise, the roll angular velocity Ω_(y) (and more precisely the corresponding components in the first and second detection directions x₁, x₂), generate a Coriolis force on the sensing masses 22 a-22 b directed along the vertical axis z, which determines rotation thereof out of the plane of the sensor xy. Instead, the configuration of the elastic anchoring elements 18 a, 18 b is such as to inhibit, to a good approximation, movement of the driving mass 13 out of the plane of the sensor xy, thus enabling effective uncoupling of the detection motion of the sensing masses with respect to the driving motion. The displacement of the sensing masses 22 a-22 d out of the plane of the sensor xy causes a differential capacitive variation of the sensing capacitors associated to the same detection direction, which can hence be determined via an appropriate reading interface, operating according to a differential scheme.

Furthermore, a yaw angular velocity Ω_(Z), acting about the vertical axis z, generates a centrifugal force (designated by F) on the further sensing masses 28, 28′ directed in a radial direction (hence directed as a centripetal force acting on the same masses), thus causing a displacement thereof in phase opposition in the radial direction. The value of the capacitive variation of the corresponding sensing capacitors is proportional to the angular velocity to be detected, which can hence be determined via the reading interface, operating once again according to a differential scheme.

The described MEMS structure 10 has a number of advantages. In particular, the configuration of the sensing masses 22 a-22 d (inclined with respect to the reference axes in the plane of the sensor) enables optimization of the exploitation of the area available for detection, increase in the sensitivity of the sensor, and improvement of the uniformity of the electrical characteristics and the robustness of the system to disturbance, thanks to the possibility of obtaining a substantial symmetry of the electrical connections to the die pads 12 d.

However, the present Applicant has found that the structure described does not enable use of a traditional reading interface (for example, of the type described with reference to FIG. 1), on account of the fact that each of the sensing masses 22 a-22 d is affected both by the pitch angular velocity Ω_(x) and by the roll angular velocity Ω_(y), in so far as both of the angular velocities determine a non-zero velocity component in the first and second detection directions x₁, x₁. Instead, the reading circuit 1 described with reference to FIG. 1 has transduction chains that are totally distinct for each pair of sensing masses and that are to detect a respective angular velocity of pitch or roll, in so far as it presupposes that the sensing masses 22 a-22 c of a first pair are affected only by the pitch angular velocity Ω_(x), and that in the same way the sensing masses 22 b-22 d of the second pair are affected only by the roll angular velocity Ω_(y).

The present Applicant has hence found that a purposely designed reading interface able to discriminate, in the capacitive variation (or, likewise, in the variation of the amount of charge) associated to the sensing masses 22 a-22 d, the contribution due to the pitch angular velocity Ω_(x) (from that due to the roll angular velocity Ω_(y), allows one to fully exploit the advantages of the MEMS structure 10.

FIG. 3 shows a schematic and simplified representation of the MEMS structure 10 of the multi-axis capacitive gyroscope previously described in detail, as regards the sensing masses 22 a-22 d, here represented simply by means of the respective fixed electrodes, designated by A, B, C and D, for detection of the angular velocities of pitch Ω_(x) and roll Ω_(y), here indicated simply by the respective vectors P and R acting along the respective reference axes of pitch (first horizontal axis x) and roll (second horizontal axis y). The sensing masses 22 a-22 d are aligned in pairs in the detection directions x₁, x₂, inclined by the angle Θ (assumed equal to)45° with respect to the pitch and roll reference axes. Moreover, designated by Ā, B, C and D are the angular velocity vectors acting on the respective sensing masses 22 a-22 d in the detection directions x₁, x₂, given by the sum vector of the projections of the angular velocities of pitch and roll P, R in the same detection directions x₁, x₂ (in FIG. 3 these projections are indicated by P _(A), R _(A) for the sensing mass 22 a; a similar notation is subsequently used also for the other sensing masses).

By applying simple geometrical considerations, it is possible to obtain the following relations:

$\overset{\_}{A} = {{{\overset{\_}{P}}_{A} + {\overset{\_}{R}}_{A}} = {{{\overset{\_}{P} \cdot \left( {\cos\;\Phi} \right)} + {\overset{\_}{R} \cdot \left( {\sin\;\Phi} \right)}} = {{\frac{1}{\sqrt{2}} \cdot \overset{\_}{P}} + {\frac{1}{\sqrt{2}} \cdot \overset{\_}{R}}}}}$ $\overset{\_}{B} = {{{\overset{\_}{P}}_{B} + {\overset{\_}{R}}_{B}} = {{{{- \overset{\_}{P}} \cdot \left( {\sin\;\Phi} \right)} + {\overset{\_}{R} \cdot \left( {\cos\;\Phi} \right)}} = {{{- \frac{1}{\sqrt{2}}} \cdot \overset{\_}{P}} + {\frac{1}{\sqrt{2}} \cdot \overset{\_}{R}}}}}$ $\overset{\_}{C} = {{{\overset{\_}{P}}_{C} + {\overset{\_}{R}}_{C}} = {{{{- \overset{\_}{P}} \cdot \left( {\cos\;\Phi} \right)} - {\overset{\_}{R} \cdot \left( {\sin\;\Phi} \right)}} = {{{- \frac{1}{\sqrt{2}}} \cdot \overset{\_}{P}} - {\frac{1}{\sqrt{2}} \cdot \overset{\_}{R}}}}}$ $\overset{\_}{D} = {{{\overset{\_}{P}}_{D} + {\overset{\_}{R}}_{D}} = {{{\overset{\_}{P} \cdot \left( {\sin\;\Phi} \right)} - {\overset{\_}{R} \cdot \left( {\cos\;\Phi} \right)}} = {{\frac{1}{\sqrt{2}} \cdot \overset{\_}{P}} - {\frac{1}{\sqrt{2}} \cdot \overset{\_}{R}}}}}$

It follows that each sensing mass 22 a-22 d generates, following upon its movement, a capacitive variation (which is proportional, as has been said previously, to the angular velocity sensed thereby in the respective detection direction) as a function both of the pitch angular velocity Ω_(x) and of the roll angular velocity Ω_(y).

The present Applicant has also realized that there exist a particular combinations of the contributions of angular velocity (and consequently of the associated capacitive contributions) acting on the four sensing masses 22 a-22 d such as to enable the desired angular velocities acting along the pitch and roll reference axes to be obtained. In particular, it is possible to obtain a total contribution of roll angular velocity by means of the following first combination expression:

$\begin{matrix} {{\overset{\_}{A} + \overset{\_}{B} - \overset{\_}{C} - \overset{\_}{D}} = {{\frac{1}{\sqrt{2}}\overset{\_}{P}} + {\frac{1}{\sqrt{2}}\overset{\_}{R}} - {\frac{1}{\sqrt{2}}\overset{\_}{P}} + {\frac{1}{\sqrt{2}}\overset{\_}{R}} -}} \\ {\left( {{{- \frac{1}{\sqrt{2}}}\overset{\_}{P}} - {\frac{1}{\sqrt{2}}\overset{\_}{R}}} \right) - \left( {{\frac{1}{\sqrt{2}}\overset{\_}{P}} - {\frac{1}{\sqrt{2}}\overset{\_}{R}}} \right)} \\ {= {2\sqrt{2}\overset{\_}{R}}} \end{matrix}$ and likewise a total contribution of pitch angular velocity, by means of the following second combination expression:

$\begin{matrix} {{\overset{\_}{A} - \overset{\_}{B} - \overset{\_}{C} + \overset{\_}{D}} = {{\frac{1}{\sqrt{2}}\overset{\_}{P}} + {\frac{1}{\sqrt{2}}\overset{\_}{R}} - \left( {{{- \frac{1}{\sqrt{2}}}\overset{\_}{P}} + {\frac{1}{\sqrt{2}}\overset{\_}{R}}} \right) -}} \\ {\left( {{{- \frac{1}{\sqrt{2}}}\overset{\_}{P}} - {\frac{1}{\sqrt{2}}\overset{\_}{R}}} \right) + {\frac{1}{\sqrt{2}}\overset{\_}{P}} - {\frac{1}{\sqrt{2}}\overset{\_}{R}}} \\ {= {2\sqrt{2}\overset{\_}{P}}} \end{matrix}$

The two previous combination expressions, in addition to enabling the useful information for each reference axis of interest to be obtained (axes of pitch and roll), afford the advantage of increasing the sensitivity of the multi-axis gyroscope, given the same area used for the sensing structure, by a factor of √{square root over (2)} (the sensitivity being in fact equal to 2·R for the axis of roll and 2·P for the axis of pitch, in structures of a traditional type).

An aspect of the present disclosure hence envisages a circuit implementation, with purposely modifications to the reading interface of the MEMS gyroscope (which once again includes a measurement chain for DSB-SC signals, followed by a measurement chain for baseband signals), of the aforesaid combination expressions, in particular by appropriately combining together electrical quantities associated to the displacements of sensing masses 22 a-22 d not referred to the same detection direction x₁, x₂ (or, likewise, referred to different detection directions). In this way, it is possible to obtain at output, after the subsequent processing operations, electrical signals directly proportional to the sole roll or pitch angular velocities, which are to be detected. In particular, these electrical quantities can be advantageously combined before processing carried out by the measurement chains for baseband signals of the transduction chain in the reading circuit, so as to obtain electrical signals that can subsequently be appropriately processed (in a traditional way) in the baseband.

As will be illustrated in detail hereinafter, an aspect of the present disclosure hence envisages introduction into the reading circuit of the MEMS gyroscope, of an additional combination stage, designed to implement the appropriate combination of electrical quantities associated to the various sensing masses 22 a-22 b in such a way as to extrapolate the information useful for detection of the sole angular velocities of roll Ω_(x) and pitch Ω_(y).

In detail, FIG. 4 (where elements that are similar to others already described previously are designated by the same reference numbers and will not be described in detail again) shows a reading circuit 30 according to a first embodiment of the present disclosure, where the aforesaid combination stage, designated by 32, is set upstream of the entire transduction chain (i.e., upstream of the charge amplifier 2 of the measurement chain for DSB-SC signals), and has inputs directly connected to the electrodes of the MEMS structure 10.

In a way similar to what is illustrated in FIG. 3, the fixed electrodes corresponding to the sensing masses 22 a-22 d are designated by A, B, C and D, on the hypothesis that associated to each of the sensing masses is a single fixed electrode; again illustrated are also the sensing capacitors with opposite capacitive variations formed between the fixed electrodes of sensing masses aligned in a same detection direction x₁, x₂, and the common mobile electrode Rot (the mobile electrode being electrically connected to the sensing masses).

The combination stage 32 also receives at input from a timing circuit (not illustrated) a first phase signal φ_(R) and a second phase signal φ_(P), in particular square-wave signals in phase opposition with respect to one another, and is configured, by means of activation of suitable switches, appropriately sized and controlled by the aforesaid phase signals, so as to short-circuit in pairs to one another the fixed electrodes A, B, C and D. In particular, the combination stage 32 implements appropriate combinations of the charge contributions (or of the capacitive variation) generated by the sensing masses 22 a-22 b, to enable detection, by means of a subsequent processing of a first combination, of the angular velocity about the roll reference axis in a first reading phase, and to enable detection, by means of a subsequent processing of a second combination, the angular velocity about the pitch reference axis in a second reading phase, distinct from the first reading phase.

In greater detail, with reference also to FIG. 5, the combination stage 32 comprises an array of switches, namely: a first switch 34, connected between the fixed electrode A (associated to the sensing mass 22 a) and the fixed electrode B (associated to the sensing mass 22 b), and controlled by the first phase signal φ_(R); a second switch 35, which is connected between the fixed electrode C (associated to the sensing mass 22 c) and the fixed electrode D (associated to the sensing mass 22 d) and which is also controlled by the first phase signal φ_(R); a third switch 36, which is connected between the fixed electrode B and the fixed electrode C and is controlled by the second phase signal φ_(P); and a fourth switch 37, which is connected between the fixed electrode A and the fixed electrode D and which is also controlled by the second phase signal φ_(P).

In addition, the combination stage 32 implements a direct electrical connection between the fixed electrode A and a non-inverting input of the charge amplifier 2, and a further direct electrical connection between the fixed electrode C and an inverting input of the same charge amplifier 2.

In use, in a first reading phase, corresponding to the high active interval of the first phase signal φ_(R), the fixed electrodes A and B are shorted to one another (and are moreover connected to the non-inverting input of the charge amplifier 2), and the fixed electrodes C and D are shorted to one another (and are moreover connected to the inverting input of the charge amplifier 2). In the first phase, given also the relation of direct proportionality between the contributions of angular velocity and the charge contributions or capacitive variations, the aforesaid first combination expression Ā+ B− C− D is thus implemented, to obtain at output from the charge amplifier 2 a signal of voltage variation correlated to the sole roll angular velocity Ω_(x).

In a second reading phase, subsequent to and distinct from the first phase, corresponding to the high active interval of the second phase signal φ_(P) (during which the first phase signal φ_(R) is at the low logic level), the fixed electrodes A and D (which are moreover connected to the non-inverting input of the charge amplifier 2) are instead shorted to one another, and the fixed electrodes B and C (which are moreover connected to the inverting input of the charge amplifier 2) are shorted to one another. In the second phase, the aforesaid second combination expression Ā− B− C= D is hence implemented, to obtain at output from the charge amplifier 2 a voltage-variation signal correlated to the sole pitch angular velocity Ω_(y).

It may hence be noted that the array of switches in the combination stage 32 implements a sort of array of weights for the combination of the fixed electrodes A, B, C and D and of the corresponding capacitive contributions, determining the sign, positive or negative, of the charge contributions associated to these electrodes in the summation generating the aforesaid first or second combination expression.

As illustrated in FIG. 4, the differential signal of voltage variation at output from the charge amplifier 2 is sent to the demodulator 4, which carries out coherent demodulation thereof using the clock signal CK in phase with the driving angular velocity ω_(z).

The reading circuit 30 hence advantageously envisages in this case a single measurement chain for DSB-SC signals, designated as a whole by 40 and constituted by the single charge amplifier 2 and by the single demodulator 4, connected in cascaded fashion. This single measurement chain provides in fact a time-division reading (timed by the aforesaid first and second phase signals) of the roll and pitch reference axes: in particular, during the first phase, the demodulated signal (at output from the demodulator 4) represents the roll angular velocity that is to be detected, whereas, during the second phase, the demodulated signal represents the pitch angular velocity.

Possibly (in a way not illustrated), the single measurement chain for DSB-SC signals 40 may be used also for time-division reading of the yaw angular velocity Ω_(z) (corresponding to the yaw reference axis), by simply introducing a third reading phase (and a third phase signal φ_(Y)) dedicated thereto, that will be shifted with respect to the previous reading phases (associated to the phase-signals φ_(R) and φ_(P)); in this case further switches will be provided, controlled by the third phase signal φ_(Y) to connect to the inputs of the charge amplifier 2 the fixed electrodes 25 associated to the further sensing masses 28, 28′, sensitive to the yaw angular velocity Ω_(z). In this third step, the switches 34, 35, 36 and 37 are open; consequently, to prevent the fixed electrodes A, B, C and D from remaining floating, a further four switches are introduced, respectively connected between the fixed electrodes A, B, C, D and a terminal at a known potential (preferably the same potential used as input common mode of the charge amplifier 2 during the first and the second reading phases) so as to keep the microelectromechanical structure completely biased.

Downstream of the demodulator 4, there is instead again envisaged the use of two distinct measurement chains for baseband signals 38 a, 38 b for the signals corresponding to the angular velocities of pitch and roll, respectively, each chain comprising a respective sample & hold stage 6, cascaded by a filter stage 8, designed to supply on the purposely provided output electrode 9 a, 9 b the useful analog output signal, containing the desired information of the pitch or roll angular velocity detected by the MEMS structure 10.

In particular, the reading circuit 30 comprises in this case a demultiplexer 39, which has its inputs connected to the differential output of the demodulator 4, also receives the first and second phase signals φ_(R), φ_(P), and is configured in such a way as to connect the output of the demodulator 4 to the first measurement chain for baseband signals 38 a (corresponding to the pitch angular velocity) during the first reading phase, and to the second measurement chain for baseband signals 38 b (corresponding to the roll angular velocity) during the second reading phase.

Advantageously, and as is evident from the foregoing discussion, the first embodiment described enables reduction of the area occupation and consumption of electric power of the reading circuit 30 associated to the MEMS structure 10 of the multi-axis gyroscope in so far as it envisages the use of just one measurement chain for DSB-SC signals. However, this solution also involves the fact that the demodulation, at least in the case of a biaxial gyroscope, occurs with a halved number of samples (in so far as the angular velocities of pitch and roll are read alternately, and the single measurement chain for DSB-SC signals is used in time division).

A second embodiment of the reading circuit, here designated by 30′ (see FIG. 6) hence envisages the use of two distinct measurement chains for the DSB-SC signals, designated by 40 a, 40 b (or possibly, in a way not illustrated, of three distinct measurement chains, in the case of a triaxial gyroscope), respectively for the DSB-SC signals corresponding to the angular velocities of pitch and roll, each chain comprising a respective charge amplifier 2 and a respective demodulator 4, cascaded together.

The combination stage, here designated by 32′, is positioned downstream of the demodulators 4 of the two measurement chains for DSB-SC signals 40 a, 40 b, and has its inputs connected to the differential outputs of the same demodulators 4.

In greater detail, the first measurement chain for DSB-SC signals, designated by 40 a, is connected at input to the fixed electrodes A and C and acquires and processes jointly the capacitive contributions associated to the sensing masses 22 a and 22 c of the first pair of sensing masses aligned in the first detection direction x₁. In particular, the charge amplifier 2 of the first measurement chain has its non-inverting input connected to the fixed electrode A and its inverting input connected to the fixed electrode C so as to supply at output a voltage-variation signal, of a fully-differential type, correlated to the difference (A-C) of the capacitive contributions associated to these electrodes.

In a similar way, the second measurement chain for DSB-SC signals 40 b is connected at input to the fixed electrodes B and D and acquires and processes jointly the capacitive contributions associated to the sensing masses 22 b and 22 d of the second pair of sensing masses aligned in the second detection direction x₂. In particular, the charge amplifier 2 of the second measurement chain has its non-inverting input connected to the fixed electrode B and its inverting input connected to the fixed electrode D so as to supply at output a voltage-variation signal, of a fully-differential type, correlated to the difference (B-D) of the capacitive contributions associated to these electrodes.

The combination stage 32′ here comprises an adder circuit of a switched-capacitor type, of a known type and hence not described in detail, which processes the signals received at input and combines them appropriately in such a way as to implement again the aforesaid first and second combination expressions. In particular, the combination stage 32′ implements simultaneously an operation of sum of the signals received at input for generating at output a first processed signal associated to the first combination expression, Ā+ B− C− D, and an operation of difference of the same signals for generating at output a second processed signal, associated to the second combination expression, Ā− B− C+ D. Note that, in this second embodiment, unlike the previous one, the combination stage 32′ is configured so as to process jointly the voltage signals at output from the demodulator blocks, and not directly the charge packets received from the sensing masses.

The processed signals, which are again of a differential type, at output from the combination stage 32′, are again processed in two distinct measurement chains for baseband signals, designated once again by 38 a, 38 b, corresponding to the angular velocities of pitch and roll, respectively. In particular, the first processed signal associated to the first combination expression, Ā+ B− C− D, hence representing just the roll angular velocity Ω_(x), is sent to the second measurement chain for baseband signals 38 b, which amplifies, filters and transforms the signal into a continuous-time signal, and supplies on the second output electrode 9 b a signal directly correlated to the same roll angular velocity Ω_(x). The second processed signal, associated to the second combination expression, Ā− B− C+ D, hence representing just the pitch angular velocity Ω_(y), is instead sent to the first measurement chain for baseband signals 38 a, which amplifies, filters and transforms the signal into a continuous-time signal, and supplies on the first output electrode 9 a a signal correlated to the pitch angular velocity Ω_(y).

Advantageously, and as is evident from the foregoing discussion, the second embodiment described enables a demodulation to be carried out with a maximum number of samples (in so far as it uses two distinct measurement chains both for the DSB-SC signals and for the baseband signals), but has the drawback of requiring an increase in area and consumption as compared to the first embodiment previously described. Furthermore, it is known that processing of voltage signals is in general more burdensome, from the standpoint of resources, as compared to processing of charge packets required to obtain the same information content therefrom.

The advantages of the reading circuit for a multi-axis MEMS gyroscope provided according to the present disclosure hence emerge clearly from the foregoing description.

In particular, it is again emphasized that the proposed circuit solution makes it possible in a simple and effective way to obtain the information associated to the angular velocities to be detected about the roll and pitch reference axes, starting from detection signals associated to detection directions inclined with respect to the same reference axes, using the measurement chains for DSB-SC signals and for baseband signals required for conditioning the signals at output from the MEMS structure of the gyroscope.

The reading circuit maintains the signal-to-noise ratio unaltered, and instead increases the sensitivity of detection of the angular velocities by a factor of √{square root over (2)}.

Of the embodiments described, the one that uses multiplexing, or time-division reading, of the channels associated to the various angular velocities (first embodiment described) is particularly advantageous as regards the reduction of the consumption levels and of the area of the integrated circuit, as well as of the costs associated to its manufacturing.

The aforesaid characteristics render the multi-axis gyroscope particularly indicated for integration in an electronic device, which can be used in a plurality of electronic systems, for example, in inertial-navigation systems, automotive systems, or in systems of a portable type, such as, for example, a PDA (Personal Digital Assistant), a portable computer, a mobile phone, a digital audio player, a photographic camera or videocamera, a controller of a videogames console, the electronic device being generally able to process, store, transmit and receive signals and information.

In detail, FIG. 7 shows an electronic device 50, comprising the multi-axis MEMS gyroscope, here designated by 52 and comprising: the MEMS structure 10 previously described; the reading circuit 30 (or, likewise and in a way not illustrated, the reading circuit 30′ of the second embodiment described); and a driving circuit 53, operatively coupled to the driving assembly 14 to impart the driving movement upon the various driving masses 13 of the MEMS structure 10 and supply biasing signals to the same MEMS structure 10 (in a per-se known manner, not illustrated in detail herein).

Advantageously, the driving circuit 53 and the reading circuit 30 can be provided in completely integrated technology (for example of a CMOS or biCMOS type) and can be integrated in a further die of semiconductor material, designated as a whole by 54, which can be placed, together with the die 12 of the MEMS structure 10, within one and the same package, designated as a whole by 55 (the two dice being electrically and mechanically connected with known techniques), thus obtaining a further reduction in area occupation.

The electronic device 50 further comprises: an electronic control unit 56, for example a microprocessor, connected to the reading circuit 30, and designed to supervise general operation of the electronic device 50, for example, also as a function of the angular velocities detected and determined; an input stage 57, provided with appropriate data-input elements which can be used by a user (for example, a keypad); an output stage 58, provided with appropriate data-output elements (for example, in the form of a display); and a transmission/reception stage 59, controlled by the electronic control unit 56 for transmission and reception of data, for example with any wireless mode of a known type (such as, for example, Bluetooth, Wifi, IR, etc.).

Finally, it is clear that modifications and variations may be made to what has been described and illustrated herein, without thereby departing from the scope of the present disclosure.

In particular, it is clear that the solution described can find advantageous application also in the case where the angle of inclination between the detection directions and the reference axes is different from 45°, for example in the case where this angle is comprised between 40° and 50°; of course, the precision of the detection of the pitch and roll angular velocities will be greater for angles of inclination equal or close to the value of 45°. Alternatively, in the case where the angle of inclination differs sensibly from the value of 45°, different operations of combination of the charge contributions (or of the capacitive variations) associated to the various electrodes, or of the electrical quantities associated thereto, may be envisaged. In particular, the array of switches in the combination stage (see the first embodiment) may in this case be configured so as to associate to each electrode an appropriate weight for generating the desired combination.

Furthermore, the reading circuit previously described can be used, with appropriate modifications, in the case where two fixed electrodes in a differential configuration are associated to each sensing mass of the multi-axis gyroscope. Also in this case, in fact, a reading phase may be envisaged dedicated to each axis to be detected, with the advantage of having a single chain for DSB-SC reading for the axes read, and the associated saving in area and current; however, the increase in sensitivity by the factor √{square root over (2)} will not be obtained.

It is also evident that the reading circuit previously described can find advantageous application also in other types of multi-axis transducers (in addition to the gyroscope described), having detection directions (i.e., sensing directions of the corresponding detection elements) inclined with respect to the reference axes (i.e., the axes along which act the physical quantities to be detected and transduced); for example, this circuit can be used in axial-flux magnetometers, or else in inertial accelerometers. More in general, the reading circuit described can be used where the physical quantity to be detected can be transduced through a charge reading of a time-division fully-differential SC type.

The various embodiments described above can be combined to provide further embodiments. All of the U.S. patents, U.S. patent application publications, U.S. patent application, foreign patents, foreign patent application and non-patent publications referred to in this specification and/or listed in the Application Data Sheet are incorporated herein by reference, in their entirety. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, application and publications to provide yet further embodiments.

These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure. 

The invention claimed is:
 1. A reading circuit for a multi-axis gyroscope provided with a microelectromechanical structure configured to rotate with respective angular velocities about respective first and second reference axes, and including first and second pairs of detection elements that are sensitive along first and second detection directions, respectively, the first and second directions being different from one another, and including first and second pairs of electrodes that are configured to generate respective detection quantities including capacitive variations due to displacements of said pairs of detection elements with respect to associated pairs of fixed electrodes as a function of projections of said angular velocities in said first and second detection directions, the reading circuit comprising: a combination stage having inputs electrically connected to the pairs of fixed electrodes to receive at input said capacitive variations and is configured to combine electrically together the detection quantities generated by the first and second detection elements, so as to take into account a non-zero angle of inclination of said first and second detection directions with respect to said first and second reference axes, and is configured to implement combinations of the capacitive variations generated by said detection elements sensitive to said detection directions different from one another; and an output stage configured to provide electrical output signals based on combined detection quantities received from the combination stage, each signal being correlated to a respective one of said angular velocities; and wherein said combination stage has an input configured to receive phase signals and includes a set of switch elements configured to be driven by said phase signals to short-circuit in pairs said fixed electrodes and to implement said combinations of said capacitive variations.
 2. The circuit according to claim 1, further comprising: an input stage configured to convert said capacitive variations into modulated electrical signals and then demodulate said modulated electrical signals based on a reference signal; the output stage being configured to receive intermediate electrical signals correlated to the electrical signals demodulated by said input stage and to process said intermediate electrical signals to generate said electrical output signals; and the combination stage being upstream of said output stage and being configured to provide said intermediate electrical signals with respective information contents exclusively associated to a respective one of said angular velocities.
 3. The circuit according to claim 2, wherein said microelectromechanical structure is further provided with a driving mass, configured to be actuated at a resonance frequency and at a driving angular velocity; and wherein said input stage comprises: a charge-amplifier element configured to amplify said capacitive variations and generate said modulated electrical signals, of a DSB-SC (Dual Side Band-Suppressed Carrier) type, amplitude-modulated with a carrier correlated to said driving angular velocity; and a demodulator element cascaded to said charge-amplifier element and configured to demodulate said modulated electrical signals of a DSB-SC type; and wherein said output stage comprises: a sampler element configured to sample said intermediate electrical signals and generate sampled electrical signals; and a filter stage cascaded to said sampler element and configured to filter said sampled electrical signals, the filter stage being configured to remove at least a frequency component correlated to said resonance frequency, for generating said electrical output signals.
 4. The circuit according to claim 2, wherein said input stage comprises distinct input-measuring chains for said angular velocities, respectively, and said output stage comprises distinct output-measuring chains for said angular velocities, respectively; and wherein said combination stage is between said input stage and said output stage and includes an adder element configured to execute respective summations of the electrical signals demodulated by each of said input-measuring chains so as to generate said intermediate electrical signals.
 5. The circuit according to claim 4, wherein said adder element is a switched-capacitance adder.
 6. The circuit according to claim 4, wherein said reference axes include a pitch reference axis and a roll reference axis and the angular velocities include a pitch angular velocity and a roll angular velocity act about the pitch and roll reference axes, respectively, and the first pair of detection elements includes a first detection element and a third detection element; the second pair of detection elements includes a second detection element and a fourth detection element; the first pair of fixed electrodes includes a first electrode and a third electrode; the second pair of fixed electrodes includes a second electrode and a fourth electrode; said first detection direction and said second detection direction are inclined by an angle between 40° and 50° with respect to said pitch and roll reference axes; wherein said input stage includes: a first input-measuring chain connected to said first fixed electrode and third fixed electrode and configured to generate a first electrical signal demodulated as a function of the difference of the capacitive variations associated with said first fixed electrode and third fixed electrode; and a second input-measuring chain connected to said second fixed electrode and fourth fixed electrode and configured to generate a second electrical signal demodulated as a function of the difference of the capacitive variations associated with said second fixed electrode and fourth fixed electrode; and wherein said adder element is configured to execute a sum and a difference of said first and second demodulated electrical signals to generate first and second intermediate electrical signals, respectively, the adder element being configured to send, substantially at a same time, the first and second intermediate signals to a first one and to a second one of said output-measuring chains, respectively.
 7. The circuit according to claim 1, wherein said reference axes include a pitch reference axis and a roll reference axis and the angular velocities include a pitch angular velocity and a roll angular velocity about the pitch and roll reference axes, respectively, said first detection direction and said second detection direction being inclined by an angle between 40° and 50 with respect to said pitch and roll reference axes; the first pair of detection elements includes a first detection element and a third detection element; the second pair of detection elements includes a second detection element and a fourth detection element; the first pair of fixed electrodes includes a first electrode and a third electrode; the second pair of fixed electrodes includes a second electrode and a fourth electrode; wherein said first detection element and second detection element and said third detection element and fourth detection element are arranged on opposite sides with respect to said roll reference axis, and said first detection element and fourth detection element and said second detection element and third detection element are arranged on opposite sides with respect to said pitch reference axis; and wherein said combination stage is configured to execute a first combination operation by adding with a first sign detection quantities correlated to the detection quantities generated by said first detection element and second detection element and with a second sign, opposite to the first, detection quantities correlated to the detection quantities generated by said third detection element and fourth detection element to generate a first output signal correlated to said roll angular velocity and to execute a second combination operation by adding with said first sign detection quantities correlated to the detection quantities generated by said first detection element and fourth detection element and with said second sign detection quantities correlated to the detection quantities generated by said second detection element and third detection element for generating a second output signal correlated to said pitch angular velocity.
 8. The circuit according to claim 1, comprising: a charge-amplifier element cascaded to said combination stage; and wherein the references axes are a pitch reference axis and a roll reference axis, and the angular velocities include a pitch angular velocity and a roll angular velocity about the pitch and roll reference axes, respectively, and the structure including: the first pair of detection elements includes a first detection element and a third detection element, the third detection element sensitive in the first detection direction; the second pair of detection elements includes a second detection element and a fourth detection element, the fourth detection element sensitive in the second detection direction; the first pair of fixed electrodes includes a first electrode and a third electrode; the second pair of fixed electrodes includes a second electrode and a fourth electrode; said first detection direction and said second detection direction being inclined by an angle that is between 40° and 50° with respect to said pitch and roll reference axes; wherein said set of switch elements includes: a first switch element connected between said first fixed electrode and said second fixed electrode and controlled by a first one of said phase signals; a second switch element connected between said third fixed electrode and fourth fixed electrode and controlled by said first phase signal; a third switch element connected between said second fixed electrode and third fixed electrode and controlled by a second one of said phase signals; and a fourth switch element connected between said first fixed electrode and fourth fixed electrode and controlled by said second phase signal; and wherein said combination stage is configured to provide a direct connection between said first fixed electrode and a first input of said charge-amplifier element and a direct connection between said third fixed electrode and a second input of said charge-amplifier element.
 9. The circuit according to claim 1, further comprising: an input stage having a single input-measuring chain cascaded to said combination stage and configured to convert said combinations of capacitive variations into modulated electrical signals and then demodulate said electrical signals as a function of a reference signal; wherein said set of switch elements is configured to be driven by said phase signals to implement a respective combination of said capacitive variations for each of said angular velocities, and supply at distinct times said respective combinations of said capacitive variations to said single input-measuring chain according to a time-division scheme, as a function of a value of said phase signals.
 10. The circuit according to claim 9, wherein the output stage includes respective output-measuring chains for said angular velocities, the output-measuring chains being configured to receive the electrical signals demodulated by said single input-measuring chain and to process said demodulated electrical signals to generate said electrical output signals; the circuit further comprising: a demultiplexer stage cascaded to said single input-measuring chain and having an input configured to receive said phase signals, and configured to supply said demodulated electrical signals at output from said single input-measuring chain to a selected one of the output-measuring chains, selected between said respective output-measuring chains according to a value of said phase signals.
 11. A multi-axis gyroscope, comprising: a microelectromechanical structure configured to rotate with respective angular velocities about respective first and second reference axes, and including first and second pairs of detection elements sensitive along first and second detection directions, respectively, the first and second directions being different from one another and including first and second pairs of electrodes that are configured to generate respective detection quantities as a function of projections of said angular velocities in said first and second detection directions including capacitive variations due to displacements of said pairs of detection elements with respect to associated pairs of fixed electrodes, said first detection directions being inclined with respect to said reference axes by a non-zero angle of inclination; and a reading circuit including: a combination stage having inputs electrically connected to the pairs of fixed electrodes to receive at input said capacitive variations and is configured to combine electrically together the detection quantities generated by the first and second detection elements, so as to take into account the non-zero angle of inclination of said first and second detection directions with respect to said first and second reference axes, and is configured to implement combinations of the capacitive variations generated by said detection elements sensitive to said detection directions different from one another; and an output stage configured to provide electrical output signals based on combined detection quantities received from the combination stage, each signal being correlated to a respective one of said angular velocities; and wherein said combination stage has an input configured to receive phase signals and includes a set of switch elements configured to be driven by said phase signals to short-circuit in pairs said fixed electrodes and to implement said combinations of said capacitive variations.
 12. The gyroscope according to claim 11, wherein said reference axes include a pitch reference axis and a roll reference axis and the angular velocities include a pitch angular velocity and a roll angular velocity about the pitch and roll reference axes, respectively; wherein the first detection direction and second detection direction are inclined by an angle between 40° and 50° with respect to said pitch and roll reference axes; and wherein the micro electromechanicl structure includes: a substrate; elastic anchoring elements; first, second, third, and fourth elastic supporting elements; and a driving mass anchored to the substrate via the elastic anchoring elements, and configured to be actuated with a driving movement at a resonance frequency; said first, second, third, and fourth detection elements including first, second, third, and fourth sensing masses, respectively, the first, second, third, and fourth sensing masses being suspended within, and coupled to, said driving mass via the first, second, third, and fourth elastic supporting elements, respectively, to be fixed with respect to said driving mass in said driving movement and perform a respective detection movement in response to pitch and roll movements at said pitch and roll angular velocities, respectively.
 13. The gyroscope according to claim 12, wherein said reference axes include a yaw reference axis, along which a yaw movement at a yaw angular velocity acts, the microelectromechanical structure including: fifth and sixth elastic supporting elements; and fifth and sixth detection elements sensitive to said yaw angular velocity, the fifth and sixth detection elements including respective fifth and sixth sensing masses suspended within, and coupled to, said driving mass via the fifth and sixth elastic supporting elements, respectively, to be fixed with respect to said driving mass in said driving movement and perform a respective detection movement in response to said yaw movement at the yaw angular velocity.
 14. The gyroscope according to claim 12, wherein said first and third detection elements are aligned in said first detection direction and said second and fourth detection elements are aligned in said second detection direction.
 15. The gyroscope according to claim 12, further comprising: a first die of semiconductor material in which said microelectromechanical structure; and a second die of semiconductor material, the second die including a driving circuit configured to drive said driving mass and integrated together with said reading circuit in said second die; said first die and second die being arranged within a same package.
 16. An electronic device, comprising: a control circuit configured to manage said electronic device as a function respective angular velocities; and a multi-axis gyroscope that includes: a microelectromechanical structure configured to rotate with the respective angular velocities about respective first and second reference axes, and including first and second pairs of detection elements sensitive along first and second detection directions, respectively, the first and second directions being different from one another, and including first and second pairs of electrodes that are configured to generate respective detection quantities are configured to generate respective detection quantities including capacitive variations due to displacements of said pairs of detection elements with respect to associated pairs of fixed electrodes as a function of projections of said angular velocities in said first and second detection directions, said first detection directions being inclined with respect to said reference axes by a non-zero angle of inclination; and a reading circuit including: a combination stage having inputs electrically connected to the pairs of fixed electrodes to receive at input said capacitive variations and is configured to combine electrically together the detection quantities generated by the first and second detection elements, so as to take into account the non-zero angle of inclination of said first and second detection directions with respect to said first and second reference axes, and is configured to implement combinations of the capacitive variations generated by said detection elements sensitive to said detection directions different from one another; and an output stage configured to provide electrical output signals based on combined detection quantities received from the combination stage, each signal being correlated to a respective one of said angular velocities; and wherein said combination stage has an input configured to receive phase signals and includes a set of switch elements configured to be driven by said phase signals to short-circuit in pairs said fixed electrodes and to implement said combinations of said capacitive variations.
 17. The device according to claim 16, of a portable type, chosen from the group consisting of: a PDA (Personal Digital Assistant) device; a portable computer; a mobile phone; a digital audio player; a photographic camera or video camera; and a video game console. 